How do I make this?

[gentlevoice1]

Hey DIY'ers,

I'm in the process of making a couple of electrostatic headphones and to that end have drawn up a drawing of one of the stators (please see attachment) - I hope it's clear how it is made ... The outer frame is an ellipse and the cross-section of the rods inside the stator also are ellipses that go from one side to the other of the outer frame.

It's not entirely completed since there needs to be holes/threads to assemble the stators, as well as fixtures to fix the stators to a surrounding headphone frame. The "S" like shape may also not be the final shape: The point of it is to "stiffen" the stator rods in a non-linear way - it probably will be replaced by small "bridges" that go between the rods - but in a similar way in that these bridges will also "sink into" the rod structure. Hope you can how this may be done ...

I'm not quite sure, however, how this is best made in practice so before drawing any more I hope for your insights ... I'm considering having the stator 3D printed on a precision 3D printer (a Projet with 0.025 - 0.05 mm accuracy) and then after this molding (or maybe it's called casting?) the stators with a lost wax process using copper for the frame & rods (I'll make sure the copper cannot oxidize during the process).

I wonder, though, if there's a more feasible way to do this?

Any insights appreciated ;-)

Jesper

P.S.: the dimensions are ~111mm high, 73 mm wide & the frame is 3 mm thick on the thickest place. The rods are 1.5 * 2 mm ovals.

[sahib]

I would say save yourself a lot of bother and get it 3D printed. Life is too short. But if you want to do it manually then that is how I would do it with my modelmaking hat on.

Use plastic (pvc) channel strips. Make a pattern of the inner shape of the ellipse from mdf. Soften the plastic strip with a heat gun (gradually and very carefully) and wrap it around the pattern. You'll obviously never be able to get it in one piece and that is the point. Cut it in the middle and that will give you one half. Then do the other half and stick them together. Tetrahydrafuran will stick pvc.

Once you have the outer frame then cut and glue the rods. You'll have a hard time achieving a nice butt joint onto a semi circular surface. The pieces are far too small. But I would fill around the joints with 2 part metallic filler (Araldite does it here in the UK) and then file them using needle files. Finally sand it all down with wet'n dry to get it all nice and clean.

But as I said save yourself a lot of bother and get it 3D printed. Then finish it off by hand again using sand paper.

[JohnRoberts]

You making a couple total or a couple prototypes?

3d printing is widely used for prototyping, and predicted to take over more and more low volume manufacturing in the future.

For high volume plastic injection molding, low volume, print it... But you still need to print a proto before tooling IM.

JR

[etheory]

If I were you I'd be looking for a Hackerspace - http://hackerspaces.org/wiki/ - in Denmark and then looking to find one with an Up! http://pp3dp.com/ 3D printer to do the prototype with.

[gentlevoice1]

Hi All,

& thanks for replying & sahib for outlining a way to do this manually. Yet I don't want to do this manually - I don't think I could - my own thought has been to do it as a combination of 3D printing combined with a lost wax casting process to make the final stators (probably in copper) .... I'm not sure you noticed this last part about the casting into copper since none of you comment on it ...

Anyway, my question really is if there might be better/smarter ways of doing this than 3D printing + casting? Like e.g. CNC machining of some kind ...? In the first round I'll most likely only make a couple of stators but maybe in time more than that if there's an interest.

@etheory: Thanks for the suggestion: I know of such a place where I live ... About the UP I don't think it's sufficiently precise (0.2 mm) but I'm aware of those personal 3D printers. Hope they become more precise & accessible price-wise in the near future.

Regards,

Jesper

[sahib]

I read your message well and I am well aware that you intend to cast it out of copper.

My manual method is the only alternative to 3D printing. When I started making models/prototypes there were no such thing as 3D printers. We did everything by hand. Even up until 2000 we made consumer electronic cases etc all manually.

My method is the only alternative to 3D printing if you are going to cast it.

You can certainly get it done on the CNC but you'll need to re- mortgage your house.

If you have good metalworking skills then you can make it out of copper but if you can't work with plastic then I can't see that route viable.

[etheory]

I know of such a place where I live ...

Sorry, your signature says "Copenhagen, Denmark", so I presumed that's where you were.

[gentlevoice1]

Hi again,

@etheory: Thanks for letting me know - I've now changed my address so that it reflects where I actually am... Not Copenhagen but Aarhus and still Denmark ;-)

Do you btw know of this one:

http://3dhomemade.blogspot.dk/

Apparently 50 micron resolution ...

@sahib: Hmmmm... pre-2000 I also did most things by hand... And I'm actually quite surprised to learn what has become possible within a very short time in terms of 3D printing & now I can see that there's also CNC mills for home use ... Wow ...

Greetings,

Jesper

[sahib]

Indeed. It all became very quickly. Pre 2000 these sort of things were specialist stuff. I purchased my first flat bed cnc in '97 and even then it was a big thing to invest into a machine like that. It cost me £16,000 with the bits and bobs.  3D printers were in their infancy. You had to do a lot of hand finishing and it is still the case. But it will get better.

[gentlevoice1]

Hi again,

I'm still in the process of finding ways to make these stators. Recently, I had a stator model 3D printed by Shapeways and it looks quite like the model I uploaded except for some printing errors. I had it made in their firmest plastic, however, it's a bit too "mushy" to be used for a stator. Then there are options of bronze or silver or stainless steel but it'll probably be at least about 280 Euros for 4 stators which I find to be too much.


So now I've made a wire stretcher so that I can stretch copper wire so that it becomes completely straight - and it works.

What I'd like to do next is this:


http://www.diyaudio.com/forums/headphone-systems/132573-has-anybody-made-els-headphone-8.html#post1827710


.. but instead of the PCB like fixtures on both sides of the copper rods I'd like to "mold" or cast the rods in a solder fixture. That is:


- I make sure the wires are fixed so that they cannot move by encapsulating all but the wire ends into a gypsum mold. The wire ends are to be "cast" into the solder.

- then I e.g. either pour in heated solder or put a large amount of solder on top of the copper and then heat until it melts into the copper rods. I hope it is sort of clear how I hope to make this work ...

However, I have no experience with melting larger amounts of solder so wonder if there is a technique or maybe a solder/tin substance that is particularly suited for this?

Thanks for reading & maybe replying 

Jesper

[gyraf]

You don't want solder, you'll want clean tin. Melting point 231.93 °C

Preheat copper and form before casting to get even results.

For melting and casting, use methods from tin-soldier casting (lots of info and hobby-shops on the 'net) - or maybe something like a solder pot:
http://dx.com/p/300w-temperature-controlled-soldering-pot-blue-golden-220v-48764?item=25